Love getting new equipment, hate the break-in

You got it. Exactly. You never know... only things will change.

Most of my upgrade cycles last a couple years primarily because of this. You get a component, break it in, then start thinking of the next. All components must be in place and broken in before looking for interconnects and power cords. Many things take over 200 hours.  I have pursued high end audio for fifty years... I bet ten of them were during something breaking in. I have done extensive interconnect comparison. So, I got to know different profiles really well. Speaking of time consuming. 

Not long ago I broke in three Audio Research 160 amps consecutively. (a brand new loaner, then my own, then brand new monoblocks). It was interesting how the break-in was exactly the same for each. The same pattern, exactly. Also, yes it went through the classic flip flop around 120 hours... very common with amps and preamps, where it sounds terrible one session and glorious the next a few times. Then kind of stabilized and slowly gets better. Two hundred hours sees about 75% of the gain... but only 95% at 600 hours. Finally stabilizing completely around 1,000. 

I have an extra system of components for breakin. I have a Bluesound Node, a Schitt DAC, Schitt integrated amp, so I can break stuff in. Yes, I know you can buy a cooker... they are so expensive I just couldn’t do it.... I should have decades ago. But I didn’t. Too late now. 

“Sometimes the journey is more fun that the arrival”?   Buddha 

Yes, especially with speakers, headphones, and tubes. With headphones you can just put 'em on a stand and let 'em play music for a few days first. My experience with speakers is that I just gotta put up with some ratty sound for awhile because when it clicks in, it will be worth it, and that has always been the case. Some speakers need a week or less, some need a couple of months. 

I totally agree with @larsman, but will add phono cartridges as the worst when it comes to break in, you can usually get the jest of whether or not you will like it right off the bat but usually go south a few times and become hard to listen to before around 200 hours of running time. Enjoy the music

My experience is a little different. I find that speakers and cartridges-things with moving parts-change a bit with time. I haven't noticed a big change with electronics, and I suspect that at least some of the change is my brain acclimating itself to the sound of a new component, which is a real thing. This is one of those interesting discussions, but not worth of any unpleasantness-we are all different. One of the most foolish things i can imagine in this hobby is trying to tell someone else what they hear.